Interfacial Behavior of Modified Nicotinic Acid as Conventional/Gemini Surfactants

Chiral Self-Assembly of Biphenyl-Cored Carbohydrate Bolaamphiphiles and Molecular Dynamic Simulation-Derived Mechanistic Insights

The presence of multiple chiral centers and constitutions in carbohydrates opens up a facile access to uncover supramolecular chirality properties in self-assembled carbohydrate bolaamphiphiles. In this work, bolaamphiphiles are presented that present monosaccharide moieties at the termini of an internal p,p'-biphenyl core segment. The core segment exhibits a planar twisting, which promotes chiral self-assembly of the bolaamphiphiles. α-D-Mannopyranoside-biphenyl-mannopyranoside bolaamphiphile self-assembles with a helicity, whereas α-L-rhamnopyranoside-biphenyl-rhamnopyranoside inverts this helicity in aq. solutions. The propensity for the emerging supramolecular chirality depends on the pH of the solution, where alkaline pH retains the helicity, whereas acidic pH abolishes the same. The concentration dependence of the chiral self-assembly properties is evaluated in solution. Molecular dynamics (MD) simulation studies reveal the thermodynamic states and interactions crucial for the self-assembly of biphenyl and the correlated terphenyl bolaamphiphiles. Morphological studies by microscopies ascertain the helicities in the solid state. The multivalent presentation of α-D-mannopyranoside in the self-assembled structures permits complexation with a relevant lectin, as assessed by turbidity assays. Cytotoxicity assessments of biphenyl bolaamphiphiles on the MCF-7 cell line reveal that the α-L-rhamnopyranoside bolaamphiphile has an IC50 of 89.6 ± 3.3 µm, indicating higher toxicity compared to the α-D-mannopyranoside bolaamphiphile, which has an IC50 greater than 100 µm.

Modification of Liposomal Properties by an Engineered Gemini Surfactant

Lipid membranes form the primary structure of cell membranes and serve as configurable interfaces across numerous applications including biosensing technologies, antifungal treatments, and therapeutic platforms. Therefore, the modification of lipid membranes by additives has important consequences in both biological processes and practical applications. In this study, we investigated a nicotinic-acid-based gemini surfactant (NAGS) as a chemically tunable molecular additive for modulating the structure and phase behavior of liposomal membranes. We specifically focused on NAGS with hydrocarbon chains that mirror those of lipid molecules. By introducing NAGS to phosphatidylcholine membranes with lipids of identical and varied chain lengths or degrees of unsaturation, we demonstrated the effects of headgroup interactions and chain mismatch between NAGS and membrane lipids. Using small-angle X-ray scattering, we showed that regardless of chain compatibility or mismatch, NAGS reduced the thickness and packing density of fluid lipid membranes. Further observations by fluorescence microscopy revealed the emergence of ordered-disordered domains upon cooling to room temperature. The observed phases were quite distinct from those of lipid membranes with analogous chain compositions, emphasizing the importance of NAGS headgroup chemistry in mediating domain formation and stabilization. These findings open new possibilities for exploiting NAGS in tuning the structure and organization of liposomal membranes with potential applications in drug delivery and biomedical imaging.

The effect of structural changes on the self-assembly of novel green pyridinium-carboxylate gemini surfactants in Langmuir and Langmuir-Blodgett films

Engineered molecules with tailored molecular structures have the potential to advance various disciplines by enhancing the properties of biological membranes. In this study, we investigated the fundamental interfacial behavior of newly synthesized, water insoluble, cationic pyridinium-carboxylate based gemini surfactants (GSs) using picolinic acid (PA), nicotinic acid (NA), and isonicotinic acid (INA) and their interactions with dipalmitoylphosphatidylcholine (DPPC) in Langmuir and Langmuir-Blodgett (LB) films. Two synthetic methodologies were employed: (a) connecting two alkyl pyridinecarboxylates through the nitrogen atoms with a xylenyl spacer, namely, PAGS, NAGS1, and INAGS; and (b) dimerizing two nicotinic acid molecules through ester linkages with 1,4-benzenedimethanol, and then quaternizing the pyridine nitrogens with hexadecyl chains to yield NAGS2. A combination of Brewster angle microscopy (BAM) and atomic force microscopy (AFM) imaging techniques yielded valuable insights into the morphology of the GS films and their mixtures with DPPC. Density functional theory (DFT) calculations were used to gain further information on the GSs structures and understand their assembly. The results indicate that the film of INAGS is the most hydrophobic film, and its monolayer is the least compressible. When the nitrogen atom and a carboxylate group of the headgroup are positioned closer to each other, the GS molecules tend to form aggregates instead of a continuous film which is observed for the INAGS surfactant. This observation is consistent with the DFT energy values of pair interactions, indicating that both PAGS and NAGS1 have closely packed conformations with high stabilization energy.

Unusual Increasing Viscoelasticity of Wormlike Micelles Composed of Imidazolium Gemini Surfactants with Temperature

The viscoelasticity of wormlike micelles composed of ionic surfactants typically shows an exponential decrease with increasing temperature, which limits their application in relatively high-temperature (>90.0 °C) oilfields and the synthesis of functional materials as supramolecular templates at high temperatures. In this work, a series of imidazolium gemini surfactants, 1,9-(ethane-1,2-diyl)bis(3-alkyl-1H-imidazol-3-ium) bromide ([C_n-2-C_nim]Br₂, n = 12, 14, 16, 18, 20), were synthesized. Their surface activities and aggregation behaviors in water were studied by electrical conductivity, rheology, polarization optical microscopy, small-angle X-ray scattering, ζ potential, and hydrogen nuclear magnetic resonance measurements. [C₁₂-2-C₁₂im]Br₂ and [C₁₄-2-C₁₄im]Br₂ mainly precipitate in water. [C_n-2-C_nim]Br₂ (n = 16, 18, 20) forms lamellar liquid crystals over a large range of concentrations at low temperatures. With the increase of temperature, the lamellar liquid crystals transit to wormlike micelles. Interestingly, the viscoelasticity of the three wormlike micelles first increases to the maximum and then decreases with increasing temperature. These wormlike micelles without additives retain high viscoelasticity up to 90.0 °C or above. With the increase of the alkyl chain length of the surfactants, the transition temperature of lamellar liquid crystal to wormlike micelles and the disintegration temperature of wormlike micelles increase. The unusual increase of the viscoelasticity of wormlike micelles was due to the desorption of weakly bound counterions and the extension of the long hydrophobic chains of surfactants at high temperatures.